Mycoplasma hyopneumoniae is a ubiquitous swine respiratory pathogen. It infects the respiratory tract of swine, colonizing the trachea, bronchi, and bronchioles. The mycoplasma produces a ciliostatic factor which causes the cilia lining the respiratory passages to stop beating. Eventually, the cilia degenerate, leaving the pig prone to infection by more serious secondary pathogens. The disease caused by Mycoplasma hyopneumoniae, enzootic pneumonia, is a chronic non-fatal disease which affects swine of all ages (R. F. Ross, Mycoplasmal diseases, pp. 436-444, in A. D. Laman, et al., (eds.) Diseases of Swine, Iowa State University Press, 1986). Infected pigs show only mild symptoms of cough and fever. However, the economic impact of the disease is significant. The disease is believed to be one of the most important causes of disease-associated loss in swine (Whittlestone, pp. 133-176, in Tully and Whitcomb (eds.), The Mycoplasma Vol 2: Human and Animal Mycoplasmas, New York, Academic Press, (1979)). The disease generally results in inefficient weight gainers, and in stunted and sickly animals. Also, affected swine are often prone to secondary infection by opportunistic organisms (Burch, Pig America pp. 26-27, December, 1982).
There have been numerous attempts to provide a vaccine for protecting swine against mycoplasmal pneumonia. However, such vaccines have not been successful, and the disease remains widespread.
Several investigators have disclosed vaccines comprising recombinantly produced surface antigens of Mycoplasma hyopneumoniae, Schaller et al., U.S. Pat. No. 4,894,332, issued Jan. 16, 1990; European Patent Publication No. 283,840, published Sep. 28, 1988.
PCT Publication No. WO 86/00019, published Jan. 3, 1986, discloses a Mycoplasma hyopneumoniae vaccine comprising exclusively Mycoplasma hyopneumoniae plasma membranes, free of other cell components.
Etheridge et al., Res. Vet. Sci. 33: 188 (1982), found incomplete protection against lung colonization by Mycoplasma hyopneumoniae when a live vaccine was given intravenously, subcutaneously, or intraperitoneally.
Kristensen et al., Am. J. Vet. Res. 42:784 (1981), found no protection of swine against mycoplasmal pneumonia after injection with heat-inactivated Mycoplasma hyopneumoniae.
Ross et al., Am. J. Vet. Res 45:1899 (1984), found that use of Mycoplasma hyopneumoniae extracts prepared by a freeze-thaw procedure to immunize swine, provided only variable protection, and in some instances, enhanced lesion development was noted in immunized swine. These investigators also studied a whole-cell vaccine prepared by formalin inactivation. Formalin inactivation significantly hindered the protective immunogenicity of Mycoplasma hyopneumoniae, and this vaccine was not effective.
Yoshioka et al., U.S. Pat. No. 3,917,819, issued Nov. 4, 1975, discloses several killed Mycoplasma vaccines comprising Mycoplasma inactivated with formalin, including an inactivated vaccine for Mycoplasma hyopneumoniae. However, this vaccine was prepared by formalin inactivation.
Thus, prior studies with inactivated Mycoplasma hyopneumoniae vaccines have been unsuccessful, presumably because the conditions employed, i.e., heat treatment, formalin treatment, or freeze-thawing, destroyed the protective antigenicity potential of the organism.
Accordingly, an effective whole cell vaccine for protecting swine against mycoplasmal pneumonia comprising inactivated virulent Mycoplasma hyopneumoniae has not been developed heretofore.
This invention provides a whole-cell Mycoplasma hyopneumoniae vaccine or bacteria comprising Mycoplasma hyopneumoniae inactivated by treatment with binary ethyleneimine. In contrast with other techniques of inactivation, this method unexpectedly does not adversely affect the protective immunogenicity of the organism such that it may be formulated as an effective bacterin.